1. Field of the Invention
This invention relates broadly to hydrocarbon production from geological formations. More particularly, this invention relates to the production of natural gas where carbon dioxide is separated from the natural gas downhole and sequestered downhole.
2. State of the Art
Separation of natural gas/carbon dioxide mixtures is of key economic importance in producing gas fields with low to high carbon dioxide contents. As natural gas continues to provide an increasing share of energy needs worldwide and global warming is accepted as a reality, “green” production of natural gas is expected to assume increasing importance.
Traditionally, the separation of carbon dioxide from natural gas is carried out by absorption-distillation, chemisorption or physisorption. For example, Statoil uses amine (MEA-monoethanol amine) absorption technology to separate carbon dioxide from natural gas on an off-shore platform in the North Sea where a natural gas/carbon dioxide mixture is extracted to the surface (platform), separated at the surface, and the carbon dioxide is then compressed and injected into a saline aquifer. While this technology may be useful in very limited situations, it is expensive and unsuitable for most applications as it requires extensive quantities of MEA and energy for distillation.
For purposes herein, the terms “methane”, “natural gas” and “CH4” are used interchangeably, although technically natural gas may include gases other than methane which is typically its primary and overwhelmingly largest component.